The disclosure of Japanese Patent Application No. H11-185310 filed on Jun. 30, 1999 and that of Japanese Patent Application No. 2000-174315, filed Jun. 30, 1999, including the specification, drawings and abstract of each, are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to an internally-toothed member, and to a method and apparatus for molding same.
2. Description of the Related Art
In general, an automatic transmission employs a planetary gear unit which is composed of a sun gear, a pinion, a ring gear and a carrier. Gear elements such as the sun gear, the ring gear and the carrier are selectively operated by frictional engagement elements such as clutches and brakes, whereby a speed-change operation is made possible.
First and second rotational members in the automatic transmission are selectively coupled, for example, by engaging and disengaging a clutch. For this purpose, the clutch has a drum, a clutch hub, a plurality of clutch plates, a plurality of clutch discs, and a hydraulic servo. The drum is designed as an internally-toothed member which is coupled to the first rotational member and which is itself rotatably mounted. The clutch hub is mounted for rotation relative to the drum. The clutch plates are spline-engaged at their outer peripheral edges with the drum. The clutch discs are spline-engaged at their inner peripheral edges with the clutch hub. The hydraulic servo engages and disengages the clutch by selectively pressing the clutch plates and clutch discs together and releasing same.
The drum and the first rotational member are coupled to each other by a meshing engagement. For this purpose, a meshing portion is formed at a tip end of the drum by means of a molding method such as corrugation molding (Cam molding).
FIG. 2 is a longitudinal sectional view of the essential part of a drum having a meshing portion formed as a molded corrugation by the method of the related art. FIG. 3 is an enlarged view of the meshing portion formed as the molded corrugation by the method of the related art.
In the drawings, drum 1 is shown as composed of a tubular trunk portion 12 and an annular disc portion 13. A splined tooth 14 is formed at a predetermined position on an inner periphery of the trunk portion 12, for example, by means of cutting. A meshing portion 15 is formed at a tip end of the trunk portion 12 by means of corrugation molding. The meshing portion 15 is composed of non-worked (non-processed) portions P1 and worked (processed) portions P2. The non-worked portions P1 and the worked portions P2 are arranged alternately around the circumference with an equal spacing (pitch) therebetween. The worked portions P2, which remain equal in thickness to the non-worked portions P1, are extruded radially outwardly.
However, in the method of molding the drum 11 according to the related art, during formation of the meshing portion, the worked portions P2 are extruded radially outwardly while remaining equal in thickness to the non-worked portions P1. This leads to a corresponding increase in diameter of the drum 11 and causes enlargement of the drum 11 Further, as the worked portions P2 are extruded, step portions R1, R2 between the non-worked portions P1 and the worked portions P2 become thinner. As a result, cracks are generated in the step portions R1, R2 the drum becomes less durable. Furthermore, a corner portion Q of the inner peripheral surface of the meshing portion 15 may sag as illustrated in FIG. 3. This reduces the quality of the drum 11.
Further, a step for molding the tooth 14 and a step for extruding the worked portions P2 both require man-hours of labor to the detriment of productivity in manufacture of the drum 11. Besides, precision in positioning of the spline teeth 14 and of the meshing portion 15 suffers. As a result, the quality of the drum 11 also suffers.
Hence, slot extraction has been considered for forming the meshing portion. FIG. 4 is a longitudinal sectional view of the relevant part of a drum having a meshing portion formed by the slot extraction of the related art.
FIG. 4 drawing shows a drum 21 as being composed of a tubular trunk portion 22 and an annular disc portion 23. A spline tooth 24 is formed at a predetermined position on an inner periphery of the trunk portion 22, for example by cutting. A meshing portion 25 is formed at a tip end of the trunk portion 22 by means of slot extraction. The meshing portion 25 is composed of non-worked portions P3 and worked portions P4. The non-worked portions P3 and the worked portions P4 are arranged alternately around the circumference with equal spacing (pitch) therebetween. The worked portions P4 are punched so that slots are formed.
However, a centrifugal force is applied to the trunk portion 22 as the drum 21 rotates. Thus, if the rotational speed of the drum 21 becomes high in use in the automatic transmission the non-worked portions P3 may be deformed as shown in the drawing. As a result, the durability of the drum 21 may suffer.
Further, since the process requires a separate molding step to form the spline tooth 24 and a punching step to form the worked portions P4, the process becomes labor-intensive and the productivity in manufacture of the drum 21 suffers. Besides, precision in positioning of the spline teeth 24 relative to the meshing portion 25 is difficult to attain, to the detriment of drum quality.
Accordingly, the objective of the present invention is to provide a solution to the above-mentioned problems of the related art. Thus, it is an object of the present invention to provide an internally-toothed member, a method of molding the internally-toothed member, and an apparatus for molding the internally-toothed member such that its size can be reduced, while enhancing its quality, durability and productivity in manufacture.
To achieve the forgoing objects, according to a first aspect of the present invention, there is provided an internally-toothed member comprising a first cylinder portion and a second cylinder portion which is larger in diameter than the first cylinder portion, wherein first and second internal teeth are formed so as to protrude radially inwardly from inner peripheral surfaces of the first and second cylinder portions, respectively.
In this case, since the meshing portion is formed with the second internal teeth protruding from the inner peripheral surface of the second cylinder portion, there is no need to increase the diameter of the internally-toothed member. Accordingly, the internally-toothed member can be reduced in size.
Further, the space between the second internal teeth and the concave portion does not thin during formation of the second internal teeth. Therefore, it is possible to prevent generation of cracks and enhance durability of the internally-toothed member. In addition, since there is no sagging at the inner peripheral surface of the meshing portion, the quality of the internally-toothed member can be further enhanced.
Further, the second internal teeth portion is integrally coupled to the concave portion. Therefore, even if a centrifugal force has been applied to the internally-toothed member during rotational movement thereof, the second internal teeth portion, the concave portion and the like are not deformed. Accordingly, the durability of the internally-toothed member can be enhanced.
In the first aspect of the present invention, the internally-toothed member may be a drum of a clutch. In this case, the second teeth may be separated by axially formed grooves.
In this case, the grooves are formed in the inner peripheral surface of the second internal teeth portion so as to extend in the axial direction. Accordingly, lubricating oil circulating inside the internally-toothed member can easily be drawn out through the groove. Also, formation of the grooves leads to a corresponding decrease in weight of the internally-toothed member.
In the first aspect or the present invention, an annular flat portion may be formed as a coupling portion between the first and second cylinder portions.
In this case, it is possible to prevent plastic flow of the material from affecting the meshing portion during formation of the splines. Accordingly, the meshing portion can easily be formed.
In the first aspect of the present invention, the internally-toothed member may be a drum of a clutch for an automatic transmission. In this case, an engaging surface for a band brake may be formed on an outer peripheral surface of the first cylinder portion. Also, the first internal teeth may be splines for spline-engaging the drum with a clutch plate, and the second internal teeth may be a meshing portion for coupling the drum to another component of the automatic transmission.
In this case, since the first meshing portion can be formed by forming the convex portions so as to protrude from the inner peripheral surface of the second cylinder portion, the drum does not increase in diameter. Further, since there is no need to form the meshing portion by corrugation molding, there is no possibility of the worked portions formed by corrugation molding being extruded radially outwardly. Accordingly, the drum can be reduced in size. As a result, it is possible to prevent the drum from interfering with another component in the automatic transmission.
Also, since the drum has a tubular shape, the outer peripheral surface of the drum can be used as the engaging surface for the band brake.
According to a second aspect of the present invention, there is provided a method of forming an internally-toothed member, comprising the steps of deforming a material by causing it to undergo plastic flow so that a first cylinder portion and a second cylinder portion, which is larger in diameter than the first cylinder portion, are formed, and forming first and second internal teeth so as to protrude radially inwardly from inner peripheral surfaces of the first and second cylinder portions.
In this case, since the first and second internal teeth can be formed by a single step of roll forming machining, the man-hours of labor are decreased and, as a result, the productivity of manufacture of the internally-toothed member can be enhanced. Further, since the precision of positioning the first and second internal teeth relative to each other can be assured, the quality of the internally-toothed member can be yet further enhanced.
In the second aspect of the present invention, the blank material may be pressed against a mandrel by a plurality of pressing means which are disposed at different positions relative to the axial and radial dimensions of the mandrel.
In this case, the pressing means are disposed at different positions relative to the axial and radial dimensions of the mandrel. Therefore, the blank material is sequentially pressed against the mandrel by the pressing means and becomes thinner as roll forming machining proceeds. In this manner, the material is gradually made thinner. Thus, even in the case where the material is thick, a sufficiently thin internally-toothed member can be molded by means of roll forming machining without adversely affecting its quality.
According to a third aspect of the present invention, there is provided a molding apparatus for producing an internally-toothed member comprising a mandrel having a first tooth die portion formed to correspond to a first cylinder portion of the internally-toothed member and a second tooth die portion formed to correspond to a second cylinder portion which is larger in diameter than the first cylinder portion, a holding member for sandwiching a material blank together with the mandrel, and pressing means for pressing the material against the mandrel and deforming the material by causing it to undergo plastic flow.
In this case, since the first and second internal teeth can be formed by a single step of roll forming machining so as to correspond to the first and second tooth die portions, the man-hour requirement decreases. As a result, the productivity of the manufacture of the internally-toothed member is enhanced. Besides, since the precision of positioning between the first and second internal teeth can be assured, the quality of the internally-toothed member can be further enhanced.
In the third aspect of the present invention, a plurality of pressing means may be used. In this case, the pressing means may be disposed at different positions relative to the axial and radial dimensions of the mandrel.
In this case, since the pressing means are disposed at different locations relative to the axial and radial dimensions of the mandrel, the blank material is sequentially pressed against the mandrel and becomes thinner as roll forming machining proceeds. In this manner, the material is gradually made thinner. Therefore, even in the case where the material is thick, a sufficiently thin internally-toothed member can be molded by means of roll forming machining without adversely affecting its quality.
In the third aspect of the present invention the molding apparatus may comprise displacement processing means for radially displacing the pressing means.
In this case, since the displacement processing means radially displaces the pressing means, the precision location of the first and second internal teeth can be enhanced.
In the third aspect of the present invention, the displacement processing means may radially outwardly displace the pressing means when a step between the first and second tooth die portions approaches the pressing means.
In the third aspect of the present invention, a convex portion for bending the material towards the mandrel may be formed on a molding surface of the pressing means.
In this case, when the blank material is shaped by the convex portion of the molding surface, the outer peripheral edge of the material is curved by the convex portion into relatively close proximity to the outer peripheral surface of the mandrel. Accordingly, it is possible to reduce the tensile stress in forming a boundary portion between the trunk portion and the bottom portion. Therefore, the boundary portion between the trunk portion and the bottom portion can be made to have a sufficient thickness.
In the third aspect of the present invention, a steep incline portion for pressing the material against the step may be formed on a molding surface of the pressing means.
In this case, since the material can sufficiently be pressed against the root of the step by the steep incline portion, the precision of the first and second internal teeth is further enhanced.